Throughout this disclosure including in the claims, the expression performing an operation “on” signals or data (e.g., filtering, scaling, or transforming the signals or data) is used in a broad sense to denote performing the operation directly on the signals or data, or on processed versions of the signals or data (e.g., on versions of the signals that have undergone preliminary filtering prior to performance of the operation thereon).
Throughout this disclosure including in the claims, the noun “display” and the expression “display system” are used as synonyms.
Throughout this disclosure, the expression “encoding” of video (e.g., a video channel) denotes mapping a sequence of samples of the video to a set of values (“code values”) indicative of displayed intensities in a range from a minimum intensity (black level) to a maximum intensity, where each of the code values determines a displayed intensity of a pixel (or a color component of a pixel, or a luminance or chroma value of a pixel, or another pixel component) when the encoded video is displayed. For example, a video channel may be encoded in a linear manner (so that the code values of the encoded video channel are linearly related to displayed intensity values) or a nonlinear manner (so that the code values of the encoded video channel are nonlinearly related to displayed intensity values).
Throughout this disclosure including in the claims, the expression “encoded video” denotes video determined by one or more channels of code values, each of the channels comprising a sequence of code values. For example, conventional Rec. 709 RGB video is encoded video comprising three channels of code values: a red channel comprising a sequence of red (R) code values (red color component values), a green channel comprising a sequence of green (G) code values (green color component values), and a blue channel comprising a sequence of blue (B) code values (blue color component values). For another example, conventional YCrCb video is encoded video comprising three channels of code values: a Y channel comprising a sequence of luminance or luma code values (e.g., luminance code values (Y), each of which is a weighted sum of linear R, G, and B color components, or luma code values (Y), each of which is a weighted sum of gamma-compressed R′, G′, and B′ color components), a Cr channel comprising a sequence of Cr (chroma) code values, and a Cb channel comprising a sequence of Cb (chroma) code values.
Throughout this disclosure, the expression “white level” denotes the smallest code value (of a channel of encoded video) indicative of a pixel or pixel component (e.g., a color component of a pixel, or a luminance or chroma value of a pixel) having maximum displayed intensity when the encoded video is displayed (assuming that the displayed pixels are determined by code values of the channel that include the entire range of code values available for said channel, and code values of any other channel that determine the displayed pixels are identical for all the displayed pixels). To display the encoded video channel, a video system may map to the maximum displayed intensity (e.g., clip or compress to the maximum displayed intensity) any code values of the channel that are larger than the white level.
Throughout this disclosure, the expression “black level” denotes the largest code value (of a channel of encoded video) indicative of a pixel or pixel component (e.g., a color component of a pixel, or a luminance or chroma value of a pixel) having minimum displayed intensity when the encoded video is displayed (assuming that the displayed pixels are determined by code values of the channel that include the entire range of code values available for said channel, and code values of any other channel that determine the displayed pixels are identical for all the displayed pixels). To display the encoded video channel, a video system may map (e.g., clip or compress), to the minimum displayed intensity, any code values of the channel that are smaller than the black level.
Throughout this disclosure, the expression “standard dynamic range” or “SDR” (or “low dynamic range” or “LDR”) channel denotes a channel of encoded video (e.g., a channel of a video signal indicative of encoded video data) having bit depth equal to N (e.g., N=8), where the code values available for the channel are in a range from a black level, X (referred to herein as a “standard black level”), to a white level, Z (referred to herein as a “standard white level”), where 0<X<Z<2N−1.
Throughout this disclosure, the expression “standard dynamic range” (or “SDR” or “low dynamic range” or “LDR”) video denotes encoded video (e.g., encoded video data or a video signal indicative of encoded video data) having at least one SDR channel.
Throughout this disclosure including in the claims, the expression “standard dynamic range” (or “SDR” or “low dynamic range” or “LDR”) video system denotes a system configured to display, in response to SDR video, an image sequence (or image) whose luminance (or luma or intensity) has a dynamic range (sometimes referred to herein as a standard dynamic range). Thus, when an SDR video system displays an image sequence in response to SDR video indicative of a set of encoded video data having an SDR channel, there is at least one value in the range from 0 to X that is not used as a code value of the SDR channel, and there is at least one value in the range from Z to 2N−1 that is not used as a code value of the SDR channel.
Throughout this disclosure, the expression “extended dynamic range” (or “EDR”) channel denotes a channel of encoded video (e.g., a channel of a video signal indicative of encoded video data) having bit depth equal to N, where the code values of the channel are in a range from a minimum value, Min, to a maximum value, Max, where 0≦Min<X<Z<Max≦2N−1, where X is a standard black level, and Z is a standard white level.
Throughout this disclosure, the expression “extended dynamic range” or “EDR” video (or “high dynamic range” or “HDR” video) denotes encoded video (e.g., encoded video data or a video signal indicative of encoded video data) having at least one EDR channel. An example of HDR video is “visual dynamic range” (VDR) video, which is video data (or a video signal) capable of being displayed by a display system with the full dynamic range perceivable by a human viewer under normal display viewing conditions.
Throughout this disclosure including in the claims, the expression “extended dynamic range” (or “EDR” or “high dynamic range” or “HDR”) video system denotes a system configured to display, in response to SDR video including at least one SDR channel whose code values are in a range from a standard black level, X, to a standard white level, Z, where 0<X<Z<2N−1, an image sequence (or image) whose luminance (or luma or intensity) has a dynamic range (sometimes referred to herein as a standard dynamic range) and a standard precision (a number, Q, of quantized levels of luminance, luma, or intensity), where the system is also configured to display an image sequence (or image) whose luminance (or luma or intensity) has an extended dynamic range (greater than the standard dynamic range) and/or an increased precision (a number, Q′, of quantized levels of luminance, luma, or intensity, where Q′>Q) in response to EDR video including at least one EDR channel whose code values include a set of standard code values (in the range from the standard black level, X, to the standard white level, Z) and an additional code value set, where the additional code value set consists of at least one code value in the range Min<X (where 0≦Min), and/or at least one code value in the range Z<Max (where Max≦2N−1), where X is the standard black level, and Z is the standard white level. For example, one EDR video system may be configured to display an image sequence having an extended dynamic range in response to multi-channel EDR video all of whose channels (e.g., R, G, and B channels) are EDR channels, and to display an image sequence having a standard dynamic range in response to multi-channel SDR video all of whose channels (e.g., R, G, and B channels) are SDR channels corresponding to the EDR channels. For another example, another EDR video system may be configured to display an image sequence having an extended dynamic range in response to multi-channel EDR video including one channel (a “first” channel, e.g., a Y channel) which is an EDR channel and other channels which are SDR channels, and to display an image sequence having a standard dynamic range in response to multi-channel SDR video including one channel (corresponding to the EDR video's first channel) which is an SDR channel and other channels which are SDR channels corresponding to the EDR video's SDR channels.
Conventional standard dynamic range (SDR) video (having a bit depth equal to N) can be transmitted through and displayed by a conventional SDR video system. Typically, the bit depth N is equal to 8. One commonly used type of conventional SDR video system displays SDR video that is 8-bit YCbCr video data (i.e., each word of the YCbCr video transmitted to or through, and displayed by, the system comprises an 8-bit Y component, an 8-bit Cb component, and an 8-bit Cr component, where the Y channel determines signal luminance, and the Cb and Cr channels determine color information), with some space above white and below black reserved for signal overshoot and undershoot. In such conventional systems, the 8-bit luminance values from 1 to 254 are available for use (0 and 255 are typically illegal, and not available for use, because they are specifically used for video timing signals). However, the specified black level is typically code 16 (the code value 16 is considered to be the black level), and the specified white level is typically code 235 (the code value 235 is considered to be the white level), and code values (indicative of luminance) in the range from 1 to 15 and/or the range from 236-254 are not used to display images.
Cast into absolute units for a reference display, code 16 (in a conventional display system of the type mentioned in the previous paragraph which operates with 8 bit YCbCr video signals) represents about 0.01 cd/m2 (0.01 candelas per square meter, where the unit “candelas per square meter” is sometimes referred to as “nits) and code 235 represents about 100 cd/m2. The conventional signal encoding used to generate the coded luminance values in the range 16-235 is roughly a gamma 2.4 curve (power function with a 2.4 exponent) which approximates the human visual perception curve for this range of luminance.
Other conventional SDR video systems display SDR video that is 8-bit RGB video data, with 8-bit code values from 1 to 254 available for use in each color channel. In some implementations (or operating modes) of such systems, the specified black level of each color channel (R, G, or B) is code 16 (the code value 16 is considered to be the black level), the specified maximum level is code 235 (the code value 235 is considered to be the maximum level), and the code values in the range from 1 to 15 and the range from 236-254 are not used to display images.
The inventors have recognized that it would be desirable to utilize unused coding space of SDR video to encode EDR video that can be displayed with standard dynamic range and standard precision by SDR video systems and can be displayed with extended dynamic range and/or increased precision by EDR video systems.